The present invention relates to a velocity measurement device for measuring the velocity of a moving media in a channel, and to a method for measuring the velocity of a moving media in a channel. In particular, but not exclusively, the velocity measurement may be used to determine the flow of the media in the channel. The device and method measure the velocity using Doppler radar velocity measurement techniques.
There are many different scenarios where it can be useful to measure the flow of a moving media. One example situation is in a sewer system, where measuring the flow of sewage can help locate blockages (from slow flow), predict pumping requirements in pumping stations, predict if spills are to occur, and estimate the amount of sewage spilled where spills do occur.
Typically, the flow can be determined by measuring the velocity and depth of the media. The velocity measurement determines both the speed and direction of movement. One technique used for measuring the velocity is Doppler radar.
Known Doppler radar devices have a control unit and a measurement unit. Doppler radar devices have high power consumption, and so the control unit is typically powered by mains power. Separate connections are used to provide power from the control unit to the measurement unit, and to communicate the measured velocity between the measurement unit and the control unit.
Existing flow measurement devices including Doppler radar for the velocity measurement are bulky and difficult to move and install. This can be problematic when measurements are required in confined spaces, for example sewers, or measurements are only required on a temporary basis.
According to a first aspect of the invention, there is provided a velocity measurement device for measuring the velocity of a moving media in a channel, the velocity measurement device including a radar unit having: a radar module arranged to measure the velocity of the media using the Doppler effect; and a two wire interface to the radar unit arranged to receive power from an external power source, and provide data transfer between the radar unit and an external control unit.
Preferably, the radar unit includes: an energy store arranged to store energy; receive energy available on the two wire interface to charge the energy store; and supply stored energy to the radar module when a velocity measurement is performed.
The power delivered over the two wire interface may be insufficient to power the radar module directly, and the energy stored in the energy store over a period longer than the radar module is operated for is sufficient to power the radar module.
Preferably, the radar module may be arranged to measure the velocity of the moving media within an active period of the two wire interface, wherein the active period is divided into a first portion in which the velocity of the media is measured, and a second portion in which the measured velocity is communicated to the external control unit, and wherein the energy store is charged during at least the first portion of the active period.
Preferably, the radar unit includes: a radar unit controller arranged to: control operation of the radar unit to store energy in the energy store; determine the energy stored in the energy store; determine the proportion of the energy that can be used in a velocity measurement; and control the radar module to measure the velocity based on the determined portion of the energy that can be used.
The radar unit controller may be arranged to vary one or more of: an output power of the radar module; a measurement duration; a number of repeat readings in a measurement; an interval between repeat readings; and a number of individual transmitters and/or receivers used based on the determined portion of the energy that can be used.
The radar unit controller may be arranged to leave a minimum level of energy in the energy store, such that the measurement can be repeated without the energy store being replenished. The radar unit controller may be arranged to omit a velocity measurement if it is determined that the energy store does not have sufficient energy to power the radar module and leave the minimum level of energy in the energy store; and only charge the energy store during the measurement.
The velocity measurement device may include: an external control unit arranged to: control operation of the radar unit; and communicate with the radar unit over the two wire interface. The external control unit may include a power supply for providing power to the radar unit over the two wire interface, and powering operation of the external control unit. The power supply may be a rechargeable power supply. The power supply may be a battery.
The external control unit may be arranged to control the operation of the radar unit such that the velocity is measured intermittently, and the external control unit may be arranged to deactivate the two wire interface between velocity measurements.
The external control unit may be arranged to determine the duration between velocity measurements based on one or more of: a default value, a user input, and one or more previous velocity measurements.
The radar module may be arranged to use microwave radar to measure the velocity of the media.
The radar module may include radar means having: means for transmitting microwaves; means for detecting microwaves reflected from the moving media; and means for determining the velocity of the media based on the reflected microwaves.
The two wire interface may be arranged to carry a maximum current. The current on the two wire interface may be varied between a first current and a second current, both lower than the maximum current, to transfer data between the external control unit and the radar unit. The current on the two wire interface may be higher than the second current to indicate an error message. The current on the two wire interface may be higher than the second current when charging the energy store.
The current on the two wire interface may be modulated when the external control unit is being used to configure the radar unit prior to use.
The radar unit may include a retentive memory to store information relating to the velocity measurements. The memory may be a non-volatile random access memory.
According to a second aspect of the invention, there is provided an external control unit for controlling the operation of a radar unit arranged to measure the velocity of a moving media in a channel using the Doppler effect, the external control unit having: a two wire interface from the external control unit arranged to supply power to the radar unit, and provide data transfer between the external control unit and the radar unit.
The power supply may be a rechargeable power supply. The power supply may be a battery.
The external control unit may include: a controller arranged to: control the operation of the radar unit such that the velocity is measured intermittently; and deactivate the two wire interface between velocity measurements.
The controller may be arranged to determine the duration between velocity measurements based on one or more of: a default value, a user input, and one or more previous velocity measurements.
According to a third aspect of the invention, there is provided a velocity measurement device for measuring the velocity of a moving media in a channel, the velocity measurement device comprising: an external control unit according to the second aspect; and a radar unit arranged to measure the velocity of a moving media in a channel using the Doppler effect, the radar unit in communication with the external control unit over the two wire interface, and provided with power over the two wire interface.
According to a fourth aspect of the invention, there is provided a flow measurement device for measuring the flow rate of a media in a channel, the flow measurement device including: a level measurement device for determining the level of the media in the channel; and a velocity measurement device according to the first aspect or the third aspect, for measuring the velocity of the media in the channel, wherein the flow measurement device is arranged to determine the flow based on the measured level and the measured velocity.
According to a fifth aspect of the invention, there is provided a method of measuring the velocity of a media in a channel, the method including: at a radar unit, receiving power from an external power source over a two wire interface; with a radar module of the radar unit, measuring the velocity of the media in the channel using the Doppler effect; and transferring the measured velocity to an external control unit over the two wire interface.
The method may include at the radar unit, storing the power received over the two wire interface in an energy store; and powering the radar module of the radar unit from the energy store, wherein the power delivered over the two wire interface is insufficient to power the radar module directly, and the energy stored in the energy store over a period longer than the radar module is operated for is sufficient to power the radar module.
Each velocity measurement may occur within an active period of the two wire interface, wherein the active period is divided into a first portion in which the velocity of the moving media is measured, and a second portion in which the measured velocity is communicated to the external control unit. The method may also include charging the energy store during at least the first portion of the active period.
The method may include: determining the energy stored in the energy store; determining the proportion of the energy that can be used in a velocity measurement; and control the radar module to measure the velocity based on the determined portion of the energy that can be used.
The method may include varying one or more of: an output power of the radar module; a measurement duration; a number of repeat readings in a measurement; an interval between repeat readings; and a number of individual transmitters and/or receivers used based on the determined portion of the energy that can be used.
Determining the proportion of the energy that can be used in a velocity measurement may include leaving a minimum level of energy in the energy store, such that the measurement can be repeated without the energy store being replenished. The method may include omitting a velocity measurement if it is determined that the energy store does not have sufficient energy to power the radar module and leave the minimum level of energy in the energy store, and only charge the energy store during the first portion of the active period.
The method may include: using an external control unit to control operation of the radar unit.
The external control unit may include a power source for providing power to the radar unit over the two wire interface, and powering the control unit. The method may include: powering the radar unit from the external control unit.
The method may include: powering the external control unit with a rechargeable power supply. The method may further include: powering the control unit with a battery.
The method may include: measuring the velocity intermittently; and deactivating the two wire interface between velocity measurements.
The method may include: determining the duration between velocity measurements based on one or more of: a default value, a user input, and one or more previous velocity measurements.
The method may include using microwave radar to measure the velocity of the media.
The method may include: varying the current on the two wire interface between a first current and second current, to transfer data between the control unit and the radar unit. The method may include setting the current on the two wire interface higher than the second current, and lower than a maximum current to indicate an error message. The method may include setting the current on the two wire interface higher than the second current, and lower than a maximum current during charging of the energy store.
The current on the two wire interface may be higher than the second current when the control unit is being used to configure the radar unit, prior to use.
According to a sixth aspect of the invention, there is provided a method of measuring the flow of a moving media in a channel, the method including: measuring the level of media in the channel; measuring the velocity of the media in the channel according to the fifth aspect; and determining the flow based on the measured level and the measured velocity.
According to a seventh aspect of the invention, there is provided a machine readable medium having instructions which when read by a machine cause the machine to perform the method of the fifth or sixth aspect.
The machine readable medium referred to in any of the above aspects of the invention may be any of the following: a CDROM; a DVD ROM/RAM (including −R/−RW or +R/+RW); a hard drive; a memory (including a USB drive; an SD card; a compact flash card or the like); a transmitted signal (including an Internet download, ftp file transfer of the like); a wire; etc.
Features described in relation to any of the above aspects of the invention may be applied, mutatis mutandis, to any of the other aspects of the invention.